A large majority of US senators on Monday urged President Barack Obama to expand defense-related aid to Israel by signing a "robust" commitment to help Washington's Mideast ally combat mounting security challenges.

Eighty-three of the chamber's 100 members signed the letter to the president highlighting the need to negotiate an enhanced memorandum of understanding (MOU) with the Jewish state.

"In light of Israel's dramatically rising defense challenges, we stand ready to support a substantially enhanced new long-term agreement to help provide Israel the resources it requires to defend itself and preserve its qualitative military edge," wrote the 51 Republicans and 32 Democrats.

"Unfortunately, Israel faces a variety of threats which require increasing the resources devoted to its defense," they wrote, citing extremist group Hezbollah positioning up to 150,000 rockets and missiles to Israel's north and how the Sinai has become a "lawless haven" for militant Islamist groups.

Washington is seeking to hammer out a new 10-year defense aid package for Israel. The current MOU expires in 2018.

"We urge you to conclude an agreement with Israel for a robust new MOU that increases aid," senators said in the letter, led by Republican Lindsey Graham and Democrat Chris Coons.

Senator Ted Cruz, currently battling with billionaire Donald Trump for the Republican presidential nomination, has signed on, but independent Senator Bernie Sanders, who is challenging Hillary Clinton in the Democratic race, has not.

The United States currently provides some $3.1 billion in annual military aid to Israel, based on the pact signed in 2007 by Obama's White House predecessor George W. Bush.

The new deal would allow Israel to maintain a technological advantage over its Arab neighbors in the midst of mounting regional instability.

"Given the extraordinary levels of weapons pouring into the Middle East, Israel could quickly find itself on the wrong end of the regional military balance," the senators warned.

Current military cooperation includes aid for the "Iron Dome" air defense system, which Israel uses to intercept short-range rockets and shells threatening its territory.